1. Field of the Invention
The present invention relates to an ink, an ink-jet recording process, and an instrument making use of the ink. More particularly it relates to an ink, an ink-jet recording process, a recording unit, an ink-jet recording apparatus and an ink cartridge that are capable of achieving highly detailed and high-image quality recording not only on coated paper specially prepared for ink-jet recording but also on non-coated paper such as paper for copying, paper for reporting, bond paper or continuous slip paper, i.e., what is called a plain paper, commonly used in offices and homes, and also are suitable for a high-frequency drive ink-jet recording system that utilizes heat energy.
2. Related Background Art
Inks with greatly various manners of being composed have been hitherto reported in respect of inks for an ink-jet recording. In particular, in recent years, detailed research and developments have been made from various approaches such as composition and physical properties so that a good record can be made even on a plain paper such as paper for copying, paper for reporting, notepaper or letter paper, commonly used in offices.
In regard to an ink-jet recording also, various methods have been proposed, including a method in which electrically charged droplets are continuously generated so that a part of the droplets is used in recording, a method in which signals are imparted to a recording head having a piezoelectric device and droplets of a recording solution are generated in accordance with the signals to carry out recording, and a method in which heat energy corresponding with a recording signal is applied to a recording solution held in a chamber of a recording head and droplets are generated by the action of this energy to carry out recording.
In particular, the ink-jet recording of the type the ink is ejected utilizing a phenomenon of ink bubbling caused by heat energy, as disclosed in Japanese Patent Application Laid-open No. 54-59936, facilitates higher integration and higher densification of nozzles, and is a method that has recently attracted particular notice. However, because of the utilization of the phenomenon of bubbling, which is not utilized in other methods, this method requires more strict conditions with respect to the ink used.
Preferable conditions for the ink used in this method can be enumerated as follows:
(1) The ink has a good bubbling response to the heat energy, so that droplets can be always stably ejected from minute ejection orifices to cause no clogging.
(2) Even if a printer has been left in an uncapped state when the recording is in a pause, the ink can be stably ejected immediately after the recording is restarted. In other words, the ink in the vicinity of the ejection orifices is not easily dried, so that no clogging occurs.
(3) An image with a high quality level, free from irregular feathering can be formed, in particular, on plain paper.
(4) Print can be quickly fixed (or dried) on plain paper, and hence may not be smeared even when rubbed.
(5) The ink has a good storage stability, and the performances of ink can be maintained over a long period of time.
(6) The ink is excellent in safety such as non-toxicity and non-inflammability.
To cope with these requirements, various manners of formulation of ink have been hitherto proposed, without any particular limitation to the heat energy type in regard to the manner of ejection. For example, inks usually contain high-boiling organic solvents such as glycols for the purposes of anti-drying, anti-clogging and so forth. When recording is carried out using such inks on a plain paper having a high degree of sizing, ink does not readily penetrate into the paper and the part on which a record has been made does not dry well, so that when recorded characters or the like are touched, the hand may be stained with ink or the characters become smeared. Thus, there have been problems.
Under such circumstances, in order to increase the penetrability of ink into paper, Japanese Patent Application Laid-open No. 55-29546 proposes a method in which a surface active agent is added in ink in a large quantity. In such an instance, the following troubles have been caused: feathering occurs very frequently on some kind of paper; when filled ian ink-jet recording head, the ink recedes from the orifice surface depending on the structural conditions of the head, resulting in no ejection of ink, or on the other hand the whole of the orifice surface becomes wet, also resulting in no ejection of ink.
Japanese Patent Application Laid-open No. 56-57862 also proposes a method in which the pH of ink is set to the alkaline side. In this instance, however, there are disadvantages such that the ink is harmful when touched with hands or that poor results or obtained in view of both feathering and drying performance when the ink is used on a paper containing a certain kind of sizing agent, e.g., a neutralized paper.
Besides the foregoing, various improvements have been attempted. Up to the present, however, no ink is known which can resolve all the above problems of feathering, drying performance and safety of ink, and also the problem of clogging, even if there is no limitation that the ink is used in the heat energy type recording. In addition, it is very important, but very difficult, to design an ink that can further be capable of responding under a high frequency the phenomenon of bubbling, which is peculiar to the heat energy type recording.